This invention relates to a catalyst component for use in the polymerization of .alpha.-olefins and to a process for the polymerization of .alpha.-olefins using the same, and more particularly, it is concerned with a supported titanium catalyst component prepared by an improved process and with a process for producing a stereoregular homopolymer or copolymer of .alpha.-olefins using a catalyst system comprising the supported titanium catalyst component and an organo aluminum catalyst component.
For the stereoregular polymerization of .alpha.-olefins, it has hitherto been carried out to use a catalyst system comprising solid TiCl.sub.3, obtained by reducing TiCl.sub.4 by various methods, and an organo aluminum compound as cocatalyst. However, this method has many disadvantages on a commercial scale in that both the polymerization activity and stereoregularity of commercially available catalyst systems are low and steps for polymer deashing and for removing amorphous polymers are required. In order to overcome these disadvantages, there have been proposed processes for the polymerization of .alpha.-olefins by the use of catalyst systems comprising, by way of example, titanium catalyst components obtained by treating solids, obtained by reducing TiCl.sub.4 with organo aluminum compounds, with complexing agents and then with TiCl.sub.4 (Japanese Pat. No. 3356/1978) or by treating the solids with complexing agents and hexachloroethane (Japanese Patent Public Disclosure No. 107294/1977). In these examples, as far as solid TiCl.sub.3 is used, however, only a part of the titanium can be utilized as active catalyst and, consequently, there is not obtained such a high catalytic efficiency as to omit the deashing step.
As a desirable method for raising the polymerization activity per unit titanium, on the other hand, it has been known to disperse and support titanium compounds on other solids. Actually, in the production of polyethylene by middle or low pressure process, a high catalytic efficiency can be achieved by the use of a catalyst system comprising a titanium catalyst component (titanium compounds on various supports) and an organo aluminum compound component. A polymeric product of good quality can be produced on a commercial scale without polymer deashing step. However, in the polymerization of higher .alpha.-olefins, e.g., propylene, a high polymerization activity as well as a high stereoregularity are required, resulting in a more difficult problem than in the case of producing polyethylene by middle or low pressure process.
Of late, various improved methods have been proposed as to the stereoregular polymerization of .alpha.-olefins using a catalyst system comprising a supported titanium catalyst component and an organo aluminum catalyst component. For example, there are: (1) a method comprising using a catalyst system composed of a solid supported titanium catalyst component obtained by cogrinding an anhydrous magnesium halide and titanium halide or complex of a titanium halide and an electron donating compound, and an organo aluminum catalyst component consisting of a trialkylaluminum and electron donor (Japanese Patent Public Disclosure Nos. 16986-8/1973); (2) a method comprising using a catalyst system composed of a supported titanium catalyst component obtained in a similar manner to set forth above except in the presence of an organic solid such as durene, hexachlorobenzene or polyolefin and an inorganic solid such as lithium chloride, calcium chloride or alumina, which are substantially inert to the other compounds for composing the catalyst, and an organo aluminum catalyst component consisting of a trialkylaluminum and electron donating compound (Japanese Patent Public Disclosure No. 86482/1974); and (3) a method comprising using, in combination, a supported titanium catalyst component, obtained by contacting a magnesium alkoxide, titanium tetrahalide, electron donating compound and halosilane, and an organo aluminum catalyst component consisting of an organo aluminum compound and electron donating compound (Japanese Patent Public Disclosure No. 98076/1977).
However, the stereoregularity of a polymer produced by the use of such a catalyst system is not always satisfactory and, in particular, when using a molecular weight regulator such as hydrogen, the stereoregularity is markedly lowered. Therefore, the prior art methods are insufficient for fully omitting the step of removing amorphous polymers.